Conventionally, bicycle gear cranks include an adapter having five or six stays spaced at regular angular intervals therebetween and fixed to the crank arm or crank shaft and a plurality of chain gears mounted to the stays so that a driving force produced by pedalling is transmitted from the stays to a driving chain through the chain gear.
Such stays, however, are disposed regardless of location of each crank arm, whereby at least five or six stays are used.
Hence, the conventional gear crank has a weight corresponding to the number of stays, which has been a defect for the bicycle demanded to be lightweight.